In recent years, various types of medical analysis have become increasingly decentralized and more accessible to the patient. The testing of bodily fluids represents one example of this decentralization. Many tests that previously had to be performed at a doctor's office and perhaps even analyzed at a separate office can now be performed immediately and inexpensively in the comfort of a patient's home. One example of such a test is blood glucose monitoring, which is widely used among diabetic patients.
Optical analysis has presented itself as one convenient method for analyzing bodily fluids. In a typical optical analysis application, a certain amount of fluid is placed in a read area adapted to allow light to pass through the fluid. The light transmitted through the fluid can then be collected and analyzed, with changes in the light indicating medically significant properties of the fluid. Fluid may be directed to a read area using a “format,” or a platform for collecting and handling the fluid.
A problem arises in that the fluid volumes used for such analyses is very small-typically in the range of from about 50 nl to about 250 nl. Such a small sample volume calls for the use of a small read area or window upon which the sample is placed and through which light is passed for analysis. For example, an optical read area of about 1.0 mm is appropriate in many applications.
One result of using a small window is that a smaller optical read diameter is necessary to avoid reading the edge of the window when the goal is to take an optical reading of the sample. For example, with a 1.0 mm window, an optical read area of about 0.75 mm might be appropriate to avoid reading the window edge.
Typically, the small window and optical read diameters of optical fluid testing systems call for tight mechanical tolerances between the format and the illumination and reading device or devices, and further require a narrow light beam to ensure the beam always passes through the read window where the sample is located. For the example given above, a typical mechanical tolerance of ±0.381 mm (a combined tolerance of ±0.254 mm for the optics and format) is needed between the format and optics. When the alignment tolerances are taken into consideration, a beam diameter of only 0.369 mm (0.75 mm-0.381 mm) is required to ensure that the beam always passes through the window. It is desirable to have an easy-to-use format for the optical testing of fluids which allows for increased tolerances between the format and optics, and which further allows for the use of a wider-diameter illumination beam.
A further problem with self-testing small amounts of sample is the lack of a convenient method of lancing, harvesting, and analyzing small sample volumes. Sample volumes of 50 to 250 nl are too small for the consumer to easily see and too difficult to place into an optical format. This problem leads to the desirability of an easy-to-use format for optical testing of fluids that enables convenient harvesting of samples.